Aptamers are short single-stranded oligonucleotides, with a specific and complex three-dimensional shape, that bind to target molecules. The molecular recognition of aptamers is based on structure compatibility and intermolecular interactions, including electrostatic forces, van der Waals interactions, hydrogen bonding, and π-π stacking interactions of aromatic rings with the target material. The targets of aptamers include, but are not limited to, peptides, proteins, nucleotides, amino acids, antibiotics, low molecular weight organic or inorganic compounds, and even whole cells. The dissociation constant of aptamers typically varies between micromolar and picomolar levels, which is comparable to the affinity of antibodies to their antigens. Aptamers can also be designed to have high specificity, enabling the discrimination of target molecules from closely related derivatives.
Aptamers are usually designed in vitro from large libraries of random nucleic acids by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). The SELEX method was first introduced in 1990 when single stranded RNAs were selected against low molecular weight dyes (Ellington, A. D., Szostak, J. W., 1990. Nature 346: 818-822). A few years later, single stranded DNA aptamers and aptamers containing chemically modified nucleotides were also described (Ellington, A. D., Szostak, J. W., 1992. Nature 355: 850-852; Green, L. S., et al., 1995. Chem. Biol. 2: 683-695). Since then, aptamers for hundreds of microscopic targets, such as cations, small molecules, proteins, cells, or tissues have been selected. A compilation of examples from the literature is included in the database at the website: http://www.aptagen.com/aptamer-index/aptamer-list.aspx. However, a need still exists for aptamers that have a high binding affinity and specificity for consumer product applications, especially those containing surfactant.